The present invention relates in general to a bearing device for a spindle, for example, for a dielectric tuner in a cavity filter. The invention also relates to a cavity filter and a method for assembling the cavity filter.
In, for example, radio base stations, cavity filters are used for filtering, for example, microwaves of particular frequencies from different transmitters to a shared antenna. A hollow dielectric body, a so-called resonator, is often used in a cavity filter to produce resonance in a cavity at a particular frequency. In order to change the resonance frequency, a dielectric tuner is used in the form of a body that interacts with the resonator.
U.S. Pat. No.4,728,913, which is hereby incorporated as a reference, shows a cavity with a hollow dielectric resonator described above, and a dielectric tuner that is fixed on a spindle. By turning the spindle, the tuner can be inserted into and withdrawn from the hole in the resonator in order in this way to change the effective dielectric constant and thereby the resonance frequency. This is described in detail in the abovementioned document, and therefore does not need to be described in greater detail. The spindle for the tuner is mounted in two places through two bushes with through-holes.
During manufacture, tolerances automatically arise between the spindle and the bushes. The tolerances can lead to problems in the form of unwanted radial play that makes the construction unstable and sensitive to vibrations. The play also means that an accurate setting of required resonance frequency is difficult and time-consuming. In addition, the device in the abovementioned document does not comprise any motor for moving the tuner. Accordingly, no automatic control of the position of the tuner can be achieved, which is a great disadvantage when, for example, there is a need to jump between different frequencies in base stations for cellular telephones.
A first general aim of the present invention is to achieve a more stable mounting of a spindle using a sliding bearing, such as for a spindle that is fixed in a bearing in a cavity filter.
A second aim is to make possible improved accuracy of automatic setting of the resonance frequency in a cavity of a cavity filter.
In the description and the patent claims relating to the present invention, the term xe2x80x9cspindlexe2x80x9d is not only the general term for a spindle, that is an element that is designed to rotate or support another element that is designed to rotate, but also relates to an element that is mounted in such a way that it can be moved axially.
The present invention relates to a bearing device for a spindle, for example for a dielectric tuner in a cavity filter for electromagnetic waves, where the bearing device comprises at least two sprung tongues, each of which has a stud with a partially spherical free end, where at least two of the free ends are in contact with a sliding surface. By this means, tolerance play is avoided between the spindle and the sliding surface. As the studs are partially spherical, they resemble a ball, which, when the stud makes contact with the sliding surface, provides a desirable minimal contact surface between the stud and the sliding surface, while at the same time allowing for a certain deviation of the spindle from an ideal contact position with the sliding surface without tolerance play arising.
The tongues are preferably an integral part of the spindle and for manufacturing reasons the studs point outwards from the spindle. In this embodiment, the tongues extend essentially parallel to an axis of symmetry of the spindle and are sprung essentially radially inwards. In addition, the studs extend essentially at right angles out from the spindle. As a result of this, a spindle can be manufactured with a distance between the free ends of two studs that is larger than the corresponding dimension for a sliding bearing and yet still be able to be inserted into the sliding bearing. This greater distance is even desirable, as it guarantees that no play arises between the sliding bearing and the spindle in normal use.
In a second embodiment, the tongues are a part of a bearing rod. In addition, the studs point outwards from the bearing rod and the spindle comprises the sliding surface.
In a third embodiment, the sliding surface is an external part of the spindle and a bearing sleeve for receiving the spindle comprises the tongues with the studs, that point essentially radially inwards towards the sliding surface.
For use in, for example, a cavity filter in the form of a so-called ceramic filter, the spindle is hollow and is made of dielectric material, such as plastic, with or without some anti-friction material such as PTFE.
In order to be able to put and, if required, fix a hollow element, such as a hollow tuner, onto the spindle, the spindle comprises a first spindle part with a first section of internal threads and a second spindle part with external threads that correspond to the first section of internal threads.
The tongues are preferably arranged at a first end of the spindle. A second section of internal threads is arranged at a second end of the spindle, where the second section of internal threads is designed to be brought into engagement with a ball screw device. By means of the ball screw device, the radial play is minimized between the spindle and, for example, a motor designed for moving the spindle.
In addition, the second end of the spindle can have an outer contour that is in the shape of a regular hexagon in order to make easier the reception of a tool that helps to screw the spindle onto the ball screw device.
The number of tongues is preferably four and the spindle comprises a reinforcing element that is arranged between at least two of the tongues. By this means, two of the tongues can be sprung in order to take up the tolerance play between the spindle and the sliding bearing, while the other two tongues considerably reduce the size of unwanted spindle vibrations when the spindle is subjected to vibrations from some external source.
In a first alternative of the first embodiment, the bearing device comprises a bearing in the form of a sleeve, where the sliding surface is arranged internally in the bearing. By this means, the manufacture of the sliding surface is made easier in comparison to the sliding surface being integrated into a large and unwieldy component.
In order to be able to make contact with, for example, a wall or a casing, such as a first casing element for the cavity, the bearing comprises a collar with a ring-shaped contact surface. The bearing consists of at least one dielectric material when it is to be used in association with a cavity filter.
In a second alternative of the first embodiment, the sliding surface is integrated with the first casing element and defines a bottom hole in the first casing element. By this means, no assembly of a bearing needs to be carried out.
The sliding surface has suitably an essentially star-shaped cross-sectional contour, where the cross-sectional contour is in the shape of a symmetrical star with eight points, where the sliding surface comprises two separate surface sections in each point, which surface sections for each of the points are in contact with a respective part of one of the studs. Alternatively, the sliding surface can have an essentially square cross-sectional contour with the same effect. Both the star-shape and the square cross-sectional contour prevent the spindle rotating around its own axis of symmetry when the spindle is inserted in the bearing, if the bearing cannot be rotated.
The bearing device allows the spindle to be inserted essentially axially along an axis of symmetry of the sliding surface, while at the same time the free end of the spindle which is at least partially spherical, together with the sliding surface, allows an angle of up to 20xc2x0 between the axis of symmetry of the sliding surface and a longitudinal axis of the spindle, without contact being lost between each stud and the sliding surface. By this means, the assembly of the spindle in the sliding bearing is made even easier. In order to be able more easily to allow insertion at an angle and to improve the sliding properties of the studs and their contact with the sliding surface, the free end of each stud is essentially hemispherical. In order, in addition, to allow even greater angles between the spindle and the sliding surface, the free end of each stud has a larger spherical surface than a hemispherical surface with the same radius as the free end.
In addition, the invention relates to a cavity filter for electromagnetic waves. The cavity filter comprises:
a first casing element;
a second casing element, which, together with the first casing element, defines a cavity;
a tuner of dielectric material;
a resonator of dielectric material which is provided with a through-hole to allow the tuner to move in and out of the resonator;
a tube-shaped first support of dielectric material on a first side of the resonator;
a movable dielectric spindle, on which the tuner is arranged;
where the spindle is mounted by means of at least two sprung tongues, each of which has a stud with a free end that is at least partially spherical, where at least two of the free ends are in contact with a sliding surface. By this means, tolerance play is avoided between the spindle and the sliding surface. As the studs are partially spherical, they resemble a ball, which when the stud is in contact with the sliding surface provides a desirable minimal contact surface between the stud and the sliding surface while at the same time allowing a certain deviation of the spindle from an ideal contact position in relation to the sliding surface without a tolerance play arising.
The cavity filter preferably comprises a tube-shaped second support of dielectric material on a second side of the resonator. By this means, a cavity filter is achieved that provides faster and simpler assembly and disassembly of the cavity filter.
It is a great advantage if the tuner is essentially circular and tube-shaped with an external diameter that is smaller than a diameter of an essentially circular opening in the second casing element. By this means, the tuner or spindle to which the tuner is attached can be replaced without the second casing element needing to be removed.
The cavity filter suitably comprises a motor mounted on the second casing element, such as a stepping motor, and a ball screw device arranged between the motor and the spindle for transferring a rotational movement from the motor into a longitudinal movement of the spindle. By means of the motor, the tuning device can be set automatically when the motor is connected to a control unit. By means of the ball screw, the radial play that has arisen as a result of tolerances between the spindle and the motor for moving the tuner is reduced. Instead of a ball screw device and a stepping motor, a linear motor can be used.
According to a first embodiment of the cavity filter, the first casing element has a bottom hole and a step to receive a bearing in the form of a hollow sleeve that comprises the sliding surface. In a second embodiment, the sliding surface is an integral surface on the first casing element. In a third embodiment, the first casing element has a bottom hole for receiving a bearing rod that comprises the tongues, and the spindle comprises the sliding surface.
The invention also relates to a method for assembling the cavity filter. The method comprises the steps of:
arranging a sliding surface in a bottom hole in a first casing element;
arranging a dielectric first support against a step in the bottom hole;
arranging a dielectric resonator above the first support;
arranging a dielectric second support above the resonator;
fixing a second casing element to the first casing element in such a way that the second casing element is in contact with the second support;
inserting a spindle with a tuner through an opening in the second casing element after the second casing element has been fixed and thereafter bringing the spindle into contact with the sliding surface.
By this means, tolerance play is avoided between the spindle and the sliding surface. In addition, a quick and simple assembly of the cavity filter is achieved, that afterwards also makes possible quick disassembly of the cavity filter.
The method preferably comprises the steps of arranging a ball screw device on both the spindle and a motor, before the spindle is inserted through the opening, and arranging a bearing in the bottom hole, where the bearing comprises the sliding surface. By this means, radial play arising through tolerances between the spindle and the motor is reduced.
Alternatively, a linear motor is arranged directly on the spindle, which provides the same effect as the ball screw device.